The present invention generally relates to optical lens assemblies and, more particularly, to lens assemblies especially useful in projection televisions.
A projection television set typically includes three cathode ray tubes (CRTs), corresponding to the colors red, blue and green. A projection lens assembly uses a plurality of optics to magnify the image appearing on the CRT faceplate and project that image onto a much larger viewing screen. Typical CRTs used in projection televisions typically have a diameter of 3 to 9 inches. The image projected onto the screen generally has a size ranging from 40 to 60 inches or larger measured diagonally.
Each CRT has an associated magnifying lens system mounted adjacent to the CRT faceplate. In one illustrative system, the lens assembly is formed with at least one xe2x80x9cAxe2x80x9d optic or element, at least one xe2x80x9cBxe2x80x9d optic or element and at least one xe2x80x9cCxe2x80x9d optic or element. Regardless of the number of optics, these are generally referred to in the art as xe2x80x9cAxe2x80x9d, xe2x80x9cBxe2x80x9d and xe2x80x9cCxe2x80x9d lens groups. That is, each xe2x80x9cgroupxe2x80x9d may be comprised of one or more optics. The xe2x80x9cBxe2x80x9d lens group usually includes an optic formed of glass, while the xe2x80x9cAxe2x80x9d and xe2x80x9cCxe2x80x9d optics may be formed of plastic, such as a molded acrylic plastic. However, it should be understood that each group may comprise one or more optics formed of glass and one or more optics formed of plastic.
Assembly of the optics within the optic mounting structure has been a continuing challenge in terms of maintaining ease of assembly while also properly positioning the optics within a supporting structure, such as a generally cylindrical lens cell. The optics must be properly positioned within the lens cell to ensure proper focus and to prevent any movement of the optics relative to the lens cell especially during transit and use. Currently, during the assembly of projection television lens systems, the optics are retained within grooves or channels within the interior of the lens cell. Annular side walls of these channels include raised flats which force the edge of the optic against an opposite wall of the groove or channel. This creates an interference fit between the lens cell and the optic. Due, however, to the rigid nature of the flats used to properly position the lens, and the rigid nature of the opposing wall, the assembly forces required to fully seat the optics within the groove or channel can be exceedingly high. The high assembly force has required a specialized assembly fixture with the capability to generate high forces to seat the optics within the lens cell. As a result, this creates high mechanical stress on the assembled lens system. Also, during the act of seating an optic within the groove or channel, the optic itself may actually remove material from the raised flat and therefore improperly position the optic within the lens cell. This improper positioning can lead to potential focusing problems.
For at least these reasons, there is a continuing need for lens assemblies which address assembly difficulties and related focusing problems while, for example, maintaining relatively low cost and complexity associated with manufacturing the lens assemblies.
The present invention generally provides a lens cell, especially useful in projection televisions, including a tubular optic support structure having an interior with a longitudinal central axis and a first optic support surface extending around the longitudinal central axis. The tubular optic support structure receives a first optic having an outer circumferential edge and a mounting surface portion adjacent the circumferential edge. The mounting surface portion extends transverse to the longitudinal cental axis. A plurality of raised surface members are formed on the first optic support surface. At least one resilient member extends transverse to the longitudinal central axis and is configured to contact the first mounting surface portion of the first optic when the first optic is positioned adjacent the first optic support surface. The resilient member is configured to apply a biasing force against the first mounting surface portion along the longitudinal central axis to force the first optic against the raised surface member of the first optic support surface. The resilient nature of this member assists in lowering the required assembly forces. That is, the resilient member may first be resiliently biased in an axial direction away from the first optic during seating of the optic within the tubular optic support structure and, thereafter, maintains a biasing force against the first optic to maintain the first optic in proper position against the raised surface members.
The first optic support surface, the raised surface members and the resilient member are preferably positioned within a groove in the interior of the optic support structure. Although the resilient member may be any member which facilitates the intended function, such as metal springs, separate rubber or other elastomeric inserts or molded rubber or elastomeric members, the preferred structure is a flexible tab member in the form of a cantilever. More preferably, four cantilevered flexible tab members are used at equidistant, spaced locations surrounding the first optic. These members are molded into a wall defining a portion of the groove in which the first optic sits.
In the preferred embodiment, the lens system includes four flexible tab members at equidistant spacings, however, many configurations and different numbers of flexible tab members may be utilized in accordance with the invention. It is preferred that, regardless of the number of flexible tab members, the spacings be equidistant such that constant force is applied against the edge of the optic around the entire circumference thereof. The preferred lens system includes multiple optics and, preferably, each of the optics is mounted within the optic support structure in the above described manner. There may be instances, however, in which only certain optics need to be mounted in the above described manner depending on the application needs.
Additional objectives, advantages and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings.